1. Field of the Invention
The present invention relates to estimation of time of arrival and/or range, particularly though not solely to a method and system for estimating range based on the time of arrival of an Ultra Wide Band (UWB) signal.
2. Description of Related Art
Methods for estimating position or range are widely used in many wireless devices. For example it is known to use a pulse-based UWB transceiver system to estimate the range to an object or between devices by determining the delay between transmission and receipt of each UWB pulse, which is also known as the Time of Arrival (TOA). Such systems may be used in applications such as radar, object location or tracking, and military applications.
In FIG. 1 shows prior art system for range estimation using TOA, as disclosed by Sinan Gezici, Zhi Tian, Georgios B. Giannakis, Hisashi Kobayashi, Andreas F. Molisch, H. Vincent Poor, and Zafer Sahinoglu, in “Localization via ultra-wideband radios.” IEEE Signal Processing Magazine, vol. 22, 2005. While a number of methods of range estimation exist, the TOA method for range estimation has particular advantages when used with UWB signals. The TOA method includes sending a coded UWB pulse 100 from the transmitter. The receiver receives the reflected pulse 101, as shown in FIG. 1(a), which is smoothed using an envelope detector or a low pass filter. Then the envelope is sampled and becomes time discrete samples 102, as shown in FIG. 1(b). The TOA of each pulse is estimated based on these discrete samples, for example the number of clock pulses between transmission and receipt.
A sampling error may occur as the estimated TOA 104 may be different from the actual TOA 106, as shown in FIG. 1(c). The discrete time sampling step and low time resolution of the sampler, means a TOA between two sample points will not be identified. That is to say, that the accuracy is limited by the sampling rate. Therefore the lower the sampling rate, the bigger the possible sampling error.
Various systems have been proposed in the prior art. For example a positioning system is disclosed in U.S. Pat. No. 7,171,303 that uses a common clock unit to form the sampling basis in both the local receiver and the relative sensor. Both the local receiver and the relative sensor have the same reference during the ranging processing. In U.S. Pat. No. 7,057,553 a method for processing the positioning signals in the global positioning system (GPS) is disclosed. The method collects pseudo-range samples from positioning signals received at the ranging receiver from several satellites. U.S. Pat. No. 7,042,868 discloses a ranging method between two packet signal transceivers. The time delay or distance between two transceivers can be determined through sending and received packet signals to each other. U.S. Pat. No. 6,239,741 describes a tunnel diode detector for UWB object detection.
The present inventors have also filed Singapore Patent Application No. 200604221-2 on Jun. 23, 2006, relating to a method using a time to voltage converter to estimate the TOA.